The invention relates to a lubricant concentrate for the cold forming of metals, the concentrate having a content of polyethylene, polyacrylate and styrene/acrylic acid copolylmer, and to a method for facilitating the cold forming of metallic workpieces.
In the cold forming of metallic workpieces it is common practice to provide the workpiece with a coating of a lubricant in order to reduce the frictional resistance between the surface of the workpiece and the forming tool. Substantially two procedures are commonly used for the preparation of a workpiece for a cold forming operation. In accordance with one procedure, lubricant including high-pressure additives or viscosity regulators is used when lower forming degrees are required. The other procedure consists in first applying a resin-based lubricant film from an organic phase and then applying a lubricating oil. This procedure is normally used when severe forming operations are to be performed.
Recently, the use of lubricants for various purposes has been constantly increasing. Under severe forming conditions the aforementioned lubricant systems no longer provide satisfactory performance. Certain problems regarding environmental protection and workplace hygiene result from the frequently existing content of organic solvents. Aspects of inflammability also play an often significant role.
What is of further considerable importance in the use of lubricants is whether the lubricant film left on the workpiece after the forming operation can easily be removed, for instance, by means of an aqueous cleaning agent.
From among the resin-containing lubricants, those based on an acrylate resin are particularly important. From the EP-A-0 175 547 it is known, for instance, to use lubricants for the cold forming of metal tubes which include a dispersion of a butyl acrylate/methyl methacrylate-ester copolymer that is defined therein in greater detail.
Another lubricant for the cold forming of metals contains 10 to 35 wt-% of an acrylate-based thermosetting resin with a glass transition temperature of -10 to +25.degree. C., 3 to 15 wt-% wax and 0.5 to 5 wt-% surfactant. The weight ratio between thermosetting resin and wax should be adjusted to 2:12. The thermosetting resin represents a copolymer of different monomers with a degree of polymerization of 1000 to 50000 (DE-A-37 20 841).
Also, a concentrate for preparing a formulation suited for applying a lubricant coating, which contains a film-forming component, an olefin and a flow-control agent is known. The ratio between film-forming component and polyolefin should be in the range of from 0.25:1 to 2:1. Acrylate-based polymers and copolymers are mentioned as film-forming components. As flow-control agents, dihydric and trihydric alcohols, glycol ethers, butyl Cellolsolves, surfactants or phosphate ethers and esters can be used (WO 92/07924).
The aforementioned lubricants and lubricant concentrates have in common that they cannot satisfy the requirements put forward in practice, in particular the requirements as regards lubricity, environmental protection, work-place hygiene and removability after the forming operation.
It is the object of the invention to provide a lubricant concentrate for the formulation of a lubricant for the cold forming of metals, which also allows severe forming operations to be performed satisfactorily, is substantially aqueous and thus unobjectionable as regards environmental protection and work-place hygiene, and can easily be removed after the forming operation.